The drawback of the compact compressed air respirators used hitherto as rescue or escape apparatus is the fact that not only are nearly 80 vol. % of inert gases to be carried with the compressed air reserve available for breathing, which is carried by the user of the respirator, but also that only a few vol. % of the oxygen breathed in are utilized physiologically and the rest is blown off into the environment during breathing out. On the other hand, it is advantageous in case of compressed air respirators that no special logistics and additional apparatus components are necessary, unlike in the case of recycling respirators with CO2 absorbers, which are correspondingly also more expensive. It would be advantageous especially in rescue and escape apparatuses if either the operating time with a given compressed air cylinder were prolonged, i.e., if it were possible to improve the utilization of a given compressed air reserve, or if it were possible to reduce the weight of the apparatus and to make it more easily portable at a given duration of use by reducing the size of the cylinder.
Rescue and escape apparatuses are carried directly on the body and shall therefore be, in general, relatively light-weight and easily portable, so that they are therefore especially well suited for the indicated purpose.
A compressed air respirator, which is also said to be used as a rescue apparatus, is known from GB 2 274 249 A. The compressed air flows here from a compressed air cylinder via an outlet at a constant gas volume flow into a breathing gas reservoir, from which the user of the apparatus breathes in via a mouthpiece and into which he also breathes out. Breathing gas enriched with CO2 is released into the environment via an expiration valve, which opens when a preset pressure is reached in the breathing gas reservoir, while compressed air flows in continuously and at a constant rate from the compressed air cylinder.
The drawback of this prior-art device is that too much fresh breathing gas is made available to the user of the apparatus when he is under low to moderate physical strain due to the compressed air flowing in at a constant rate, at any rate more than is physiologically consumed, whereas a possibly substantially larger expiration volume will enter the breathing gas reservoir with increased CO2 concentration under a higher physical strain, so that the mean CO2 concentration of the gas being breathed in may increase to an undesirably high value. However, a higher setting of the constant gas volume flow into the breathing gas reservoir shortens the desired longer use time of the respirator. Efficient enrichment with CO2 of the expired air released into the environment from the deep regions of the lung is not achieved with the prior-art respirator.